I have, the "goth" kids at our school wore the typical goth spiky collar/wrist cuff things...but now and then I saw a few of them walking some of the goth girls around on leashes.
Because of their general fashion the collars and cuffs just looked like they were a part of the outfits themselves.
I do know for a fact at least one of the girls was into BDSM though.

As long as you mix it in with the right outfit and such, collars, cuffs, and even things like leather/pvc/rubber outfits are pretty easy to wear in public.
Of course, it would stand out less or more depending upon the situation and location.

i've definitely seen collars, cuffs, etc. plenty of times, usually on people dressed sort of fetishy or goth. Especially at concerts and things. But once in a while i've seen folks in regular street clothes wearing collars, usually a day collar or something similarly incognito that could be mistaken for jewelry by those not in the know, but because i'm in the lifestyle, i recognized them. i've even seen the chain and padlock style collars in public. These are a little more obtrusive but still something that most people who aren't in the lifestyle wouldn't recognize. i personally wear a necklace that symbolizes my submission in a way that no one but my Mistress and i will realize is anything but a necklace.

It's worth mentioning that i always have a little "aww" kind of moment when i see people in public that i can tell are in the lifestyle, the same way that i feel when i see other gay folks who are obvious or who are obviously in a same sex relationship or engaging in appropriate levels of public displays of affection. It's always nice to see an incognito collar or a leather flag displayed on clothing or in a tattoo or some other symbol or action that makes it obvious that they're leather folks. i never mind when i see people in fetishy outfits, that's cool too, but i love seeing people in totally plain normal clothes but wearing what i recognize as a day collar or something. Kinky people don't always look like kinky people at first glance and it's nice to see other inconspicuously kinky people.

I used to live in San Francisco, so very much yes. Especially in the Castro. But even outside very overt displays, I've learned to recognize people's stealth collars more and more

I think subtle elements mixed in with outfits can be awesome. I have to be fairly cautious about being on the dl, but I occasionally will wear a black leather bracelet on my left wrist, or a pendant that resembles a knife.

Over the years I have seen a few people wearing bondage gear. Mostly it was collars and cuffs that were worn by the Goths so I can't really say if it was fashion or not. I myself have worn both a collar a leash in public in the past. Pretty sure that since me and the guy who held the leash were also dressed Gothic/Black Metal at the time that others thought it was a fashion statement or just for "show" when it absolutely wasn't.